How Do mecanum wheels handle the bumps?

[NyCityKId]

Someone mentioned that mecanum wheels don't have good friction and that might be a problem when going over the bumps in breakaway. I wondering if we will have any problems if there is a similar obstacle in the years to come. i know mecanum wheels offer great maneuverability but i don't know if its worth the loss of ability to handle bumps and similar obstacles (assuming there is enough loss to cause concern). please list any disadvantages of mecanum wheels. thanks

feel free to IM me

[quinxorin]

Actually, mecanum wheels, at least for my team, have no trouble going over the bumps. The main reason people think they have trouble seems to be that the driver must get the robot lined up fairly straight, but 'fairly straight' appears to be about 10 degrees margin of error in each direction. Our robot can simply drive up to the bumps, and drive over, no problemo.

[Mr. Lim]

http://www.youtube.com/watch?v=PneD_4vcvxE

[NyCityKId]

thanks a lot. i will definatly look into mechanum wheels now

[alicen]

mecanum wheels are absolutely wonderful for maneuverability, as for going over the bump, they don't really have a problem as long as you're going forward and not diagonal or sideways. The only other thing is that mecanums work best when all four wheels are touching the ground at all times, so an active suspension is fairly important

hope that helps

[Drivencrazy]

When developing a design for this years robot our team questioned mecanum wheels' ability to push or pin and avoid being pushed or pinned.

In the end we decided to implement a crab drive. While slightly more complicated we felt that it would give us a pushing advantage.

My question is whether or not these asumptions were accurate and if so to what extent?

What other advantages or dissadvantages do mecanums have over some other forms of drive trains?

[NyCityKId]

Originally Posted by alicen

mecanum wheels are absolutely wonderful for maneuverability, as for going over the bump, they don't really have a problem as long as you're going forward and not diagonal or sideways. The only other thing is that mecanums work best when all four wheels are touching the ground at all times, so an active suspension is fairly important

hope that helps

what do you mean by active suspension. i thought we weren't allowed to have a suspension on this years robot...

[alicen]

mecanums make it very simple to avoid pinning by scooting off in whatever direction you choose, it is also surprising how well you can push/pin, but only in the forward direction. It's easy to be pushed when pushed from the side, but from front or back you can just strafe away. the biggest pro (to me at least) between mechs and crab is that mechs are much simple mechanically, than crab, and are usually lighter as well. over other drive trains, mechs have the maneuverability. They can go any direction they please, and turning is not difficult, like it can be for tank or skid steer.


active suspension -- basically it is some kind of force that keeps the wheels touching the ground. if there's a dip under only one wheel, the suspension pushes that wheel further down while the rest of the wheels a pulled a bit higher. Think of the shocks on a bicycle, it's a similar concept. For our team, the way we implement suspension is by using springs captured between a point on the wheel module and the frame. If you'd like, i can dig up a picture of the robot for you

[joeweber]

Mechanums can push and go over the bump very well. You do have to watch you weight distribuition though. Most videos show a stripped down robot that is not at the full weight plus battery and bumpers. A full wieght robot that is well ballanced will go right over but one that is out of ballance will struggle.

Our video http://www.youtube.com/watch?v=7_rtqg838Nc

[Ether]

Originally Posted by NyCityKId

what do you mean by active suspension

I think he just meant a working suspension.

An "active" suspension would be a pretty neat trick for a FIRST robot.

http://en.wikipedia.org/wiki/Active_suspension


~

[Kibaspirit]

Our mechanum wheels worked wonders over the bump. We lowered our center of gravity as far as possible though, to avoid tipping, and to help maneuverability over the bump.

We had no problems. [:

[Chris is me]

Originally Posted by Drivencrazy

When developing a design for this years robot our team questioned mecanum wheels' ability to push or pin and avoid being pushed or pinned.

In the end we decided to implement a crab drive. While slightly more complicated we felt that it would give us a pushing advantage.

My question is whether or not these asumptions were accurate and if so to what extent?

What other advantages or dissadvantages do mecanums have over some other forms of drive trains?

Mecanums notoriously lack "pushing power". The combination of a lower coefficient of static friction and the wheel's inherent inefficiency (Only ~71% of the output torque is transmitted in the direction of travel) would make your assumptions pretty accurate. Of course, prototyping for yourself is the best way to figure out to what extent these problems exist and whether or not you can live with them.

Mecanums generally try to avoid defense rather than overpowering it. This doesn't work particularly well in my opinion. Teams using mecanum should maximize their use in portions of the game with limited defensive interaction. For example, team 230 straddles the bump using mecanums in order to hang.

[FRC2669_Valery]

we're in team 2669 using mecanum wheels (2010 edition).

When our weight was almost the max (1-2 pounds less) we had a little problem when passing the bumpers, we needed some momentum and then it passed them nicely.

Right now, after we lost more than 20 pounds, we can stand 1mm next to the bump and then it passes it smoothly without any problems

[Kibaspirit]

For example, team 230 straddles the bump using mecanums in order to hang.

This is what we did, it worked everytime.

[joeweber]

Originally Posted by Chris is me

Mecanums notoriously lack "pushing power". The combination of a lower coefficient of static friction and the wheel's inherent inefficiency (Only ~71% of the output torque is transmitted in the direction of travel) would make your assumptions pretty accurate. Of course, prototyping for yourself is the best way to figure out to what extent these problems exist and whether or not you can live with them.

Mecanums generally try to avoid defense rather than overpowering it. This doesn't work particularly well in my opinion. Teams using mecanum should maximize their use in portions of the game with limited defensive interaction. For example, team 230 straddles the bump using mecanums in order to hang.

With our new drive design we were able to play great defense. The addtion of a set of omni wheels increased our ability to push by quit a bit. We were holding our own against standard six wheel drive robots.